The Core 2 Thermal Sensor Is 20% Off This Cyber Monday.
Black Friday sales officially kick off on Friday, November 28, and run through Cyber Monday, December 1. Before they end, Lifehacker is sharing the best sales based on product reviews, comparisons, and price tracking tools.
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The Core 2 Thermal Sensor, normally priced at $295, is now on sale for $236—20 % off on Cyber Monday. And here’s the kicker: buy it now and you’ll be ready for the spring heat when workout season arrives.
What does Core 2 do?
Core 2 is a small plastic sensor that attaches to your heart rate monitor’s chest strap and tracks your body temperature during workouts. It will help you understand how heat affects your performance and help you choose the right training protocol to adapt to extreme conditions more quickly and effectively.
My colleague Beth Skuerecki, who tested the Core 2 , noted that it was a bit complicated to set up, but once installed, it was simple and straightforward. She was most impressed by the overall picture it provides: tracking how your body adapts to heat over time.
Train hot, race cool
Core 2 data serves two main purposes. First, it helps you plan your heat acclimation training, helping you adapt to the heat more strategically. Second, it can be used during runs to monitor body temperature and prevent overheating when necessary.
As Beth notes, there’s legitimate debate about whether training in the heat is appropriate for every athlete. It’s arguable that most runners will benefit more from longer or faster runs than from adding heat stress to their training. But if you train in the heat—whether because you live in a hot climate, are training for a warm-weather race, or are intentionally heat-adapting—the Core 2 looks like it could be an incredibly useful tool.
It’s worth it for a real runner.
At nearly $300, it’s not an impulse buy. But at $236, it’s more accessible to serious athletes looking to take their heat training to the next level. Buying it now, on Cyber Monday, gives you a few months to get used to the device before spring and summer arrive. By the time racing season heats up, you’ll have a firm grasp of how your body reacts to heat stress and how to manage it.
How long do Black Friday deals actually last?
Black Friday sales officially begin on Friday, November 28, 2025, and will run throughout Cyber Week—the five-day period from Thanksgiving to Cyber Monday, December 1, 2025. However, the dates of Black Friday and Cyber Monday have been shifted as retailers compete for shoppers. You can take advantage of the same Black Friday deals early in the season , and we expect the sale to end by December 3, 2025.
Are Black Friday deals worth it?
In short, yes, Black Friday still offers deals you rarely see the rest of the year. If you’re shopping or looking for gifts, now is the time to look for deals on essentials, especially tech , home goods , and fitness equipment . Of course, if you’re looking to save money, the best way to save is to buy nothing.
Are Cyber Monday deals better than Black Friday?
Black Friday used to favor large retailers and higher-end appliances, while Cyber Monday favored cheaper appliances and gave small businesses a chance to compete online. However, today, this distinction has become virtually meaningless. Every major retailer runs sales on both days, so it’s best to know what you need, use price trackers, or consult guides like our blog , which uses price trackers, and not worry about finding the perfect time.